1. Field of the Invention
The present invention relates to a chip bonding method and apparatus and more particularly to a method and apparatus for removing a chip from a bonding stage of a bonding machine.
2. Prior Art
When bonding chips, they are vacuum-chucked from a tray for wafers or chips and then placed on a bonding stage. After being heated for a prescribed period of time on this bonding stage, the chips are bonded to lead frames. In this case the bonding stage is moved beneath the lead frame, and upon a bonding request signal (which indicates that the chip on the bonding stage is ready to be bonded) from the control circuit of a chip bonding machine, bonding is actually performed.
The temperature for heating the chips on the bonding stage is approximately 400.degree. to 500.degree. C., and the heating is performed for approximately 10 seconds. If a chip on the bonding stage is heated longer than this heating time, the chip will suffer thermal failure.
Occasionally, a chip is left on the bonding stage for more than a permissible heating time period. There are several reasons for this. In one instance, a chip is left on the bonding stage when bonding detection needs to be redone because of a lead frame detection error. When the heater of the bonding tool that performs the bonding by pressing the lead frames against the chip burns out, the chip is also left on the bonding stage. Thus, chips are left on the bonding stage because when the bonding detection is required and/or when the heater burns out as in the instances described above, the bonding operation of the chip bonding machine is halted. Accordingly, if the chips are to remain on the bonding stage longer than a predetermined heating time, it is necessary to remove the chips from the bonding stage.
FIG. 5 shows one conventional way to remove the chips from a bonding stage. In this Figure, a pusher 62 which is attached to the operating rod of a cylinder 61 is positioned on one side of a bonding stage 60, and a rescue stage 63 is installed so as to face the pusher 62 on the opposite side of the bonding stage 60. If the heating time for a chip 64 placed on the bonding stage 60 has exceeded a prescribed length, the cylinder 61 is actuated and the chip 64 is pushed and removed by the pusher 62 so as to be sent to the rescue stage 63.
In this prior art, the chip 64 on the bonding stage 60 is pushed by the pusher 62. In other words, the chip 64 is caused to slide on the surface of the bonding stage 60 and sent to the rescue stage 63. The result is that the top and bottom surfaces of the chip 64 may be contaminated, chipped or cracked, and reuse of the chip becomes impossible.
In one method to prevent the chipping, cracking, etc., chips are removed by tweezers, thus making a reuse of the chips possible. However, this method is inefficient and results in extremely poor productivity.